Infections with oncogenic types of HPV cause virtually all cases of cervical cancer worldwide. Prophylactic and or combined prophylactic and early therapeutic types of vaccination against HPV 16, the most important HPV type, could protect against a large minority of the cases of cervical cancer globally. Two vaccines are under study. The immunogenicity and safety of HPV 16 virus-like particles as antigens are being evaluated in collaborative Phase 1 and Phase 2 trials at Johns Hopkins. Immunogenicity and safety of the prophylactic vaccine have been demonstrated in work to date. Early trials of a mixed prophylactic/therapeutic vaccine are underway. A full-scale Phase 3 randomized controlled trial of the two vaccines will be fielded very soon. Costa Rica was chosen for the Phase 3 trial because of our extensive successful scientific collaborations there, the continued high risk of cervical cancer, the universal medical system providing national linkage, and the likelihood of very high participation over the many needed years of close clinical follow-up. Over 10,000 women will be vaccinated according to current plans. In support of the vaccine trials, a variety of methodologic and ancillary projects are underway or planned, that will maximize the yield of the main effort.